[Research Paper] 대한금속 ·재료학회지 (Korean J. Met. Mater.), Vol. 57, No. 4 (2019) pp.1-6 DOI: 10.3365/KJMM.2019.57.4.1

Comparative Leaching Study on Conichalcite and Chalcopyrite under Different Leaching Systems Jiajia Wu, Junmo Ahn, and Jaeheon Lee* Department of Mining and Geological Engineering, The University of , Tucson, AZ, 85721, USA

Abstract: leaching from low-grade copper samples obtained from two active mines in the US, named conichalcite (sample A) and chalcopyrite (sample B), were studied under different leaching conditions using sulfuric acid and methane sulfonic acid (MSA). The conichalcite, sample A, is -copper arsenite hydroxide [CaCu(AsO4)(OH)] with small amount of gold and other metals. The copper grade is 0.41% with 0.48% and 2.04% sulfur. The chalcopyrite, sample B, was the main mineral with 0.60% copper grade with 0.73% sulfur and 0.032% molybdenum. Leaching systems utilized two oxidants (ferric ion and peroxide) to investigate the kinetics of copper extractions. All leaching tests were performed by bottle roll leaching tests with 6.25% pulp density for 24 hours. Results showed that the leaching kinetics were relatively fast for oxidized sample A. Overall copper recovery was slightly affected by the oxidants and higher than 60% copper extraction was observed. Screen fractioned materials and the leached residue analysis showed that the copper grade in the residues are relatively consistent with 0.14-0.16% copper. This results showed that the ore samples contains readily leachable copper and refractory elements in all size fractions. The refractory portion seems to be relative uniform with wide range of easily leachable copper with 0.30 to 0.54% copper. Copper extraction from sample B using acids with ferric ion as an oxidant showed around 35% but it significantly increased over 80% using hydrogen peroxide as an oxidant. The copper extraction gradually increased up to 3.0 mol/L hydrogen peroxide content. (Received December 6, 2018; Accepted January 31, 2019)

Keywords: conichalcite, chalcopyrite, leaching, hydrogen peroxide

1. INTRODUCTION one of the primary sulfide minerals, is very difficult to leach in acidic solution at ambient temperature. Many efforts have In 2015, the copper recovered by leaching accounts for made to develop new methods to extract copper from 43% of total copper production in the US [1]. The chalcopyrite, such as utilizing bacteria or stronger oxidant hydrometallurgical process for copper recovery is well [3,4]. developed over the years because it produces less waste than The conichalcite-rich deposit where sample A was pyrometallurgy and presents great advantage in treating low- received is located at the Maggie Creek district in 's grade materials. Carlin trend, USA. It is a subhorizontal, sedimentary rock-

Conichalcite with ideal formula CaCu(AsO4)(OH) is not hosted gold and copper deposit. Although it is productive for well known. Generally, it is recognized as a secondary gold, there is large quantities of copper (150 Mt, at an mineral in the oxidized zone of copper deposits, typically an average grade of 0.25% Cu) [5,6]. In the supergene zone, alteration product of enargite. The leaching behavior of conichalcite, chrysocolla, cuprite, native Cu, chalcocite, conichalcite is not fully clarified, and it is classified as , and Cu-bearing kaolinite, montmorillonite, and refractory material under some occasions [2]. Chalcopyrite, halloysite contribute to the composition of copper ore [7]. Sample B is originated from a chalcopyrite-rich deposit, located in southern Arizona, USA. It contains one of the - *Corresponding Author: Jaeheon Lee largest supergene porphyry copper deposits in the world [8]. [Tel: +1-520-488-0853, E-mail: [email protected]] Both sulfide and oxide ores occur in the ore body and the Copyright ⓒ The Korean Institute of Metals and Materials 2 대한금속 ·재료학회지 제57권 제4호 (2019년 4월)

Table 1. Chemical analysis of sample A. (%) Cu Fe As S Al K Mg 0.41 5.36 0.48 2.04 7.04 3.03 0.31 Ti Ca Ba P Cr Pb Ni 0.26 0.28 0.21 0.16 0.06 0.04 0.02

Table 2. Rock-forming minerals of sample A. (%) Quartz Muscovite Alunite Jarosite Anhydrite Magnetite Hematite Goethite 45.5 30.7 12.4 3.5 0.8 2.5 2.5 2.1

main sulfide minerals are pyrite, chalcocite, and chalcopyrite. showed the copper content of 0.41% as listed in Table 1. The The predominant oxide minerals are chrysocolla and mineral compositions were analyzed by QEMSCAN malachite. According to Enders’s study [9], in the hypogene (Quantitative Evaluation of Mineralogy by Scanning zone, copper content in the host rocks is fairly uniform Electron Microscopy), and the results are presented in Table (0.39% Cu) but shows significant variations by rock-type. 2 and Table 3. In the ore sample, the main rock-forming Chalcopyrite averages 0.56% and ranges from 0.025 to over minerals were quartz and muscovite. Conichalcite was the 2.9%, and correlates directly with the distribution of dominant copper-bearing mineral and pyrite was the second hypogene copper grade. one with 20.83%. Chrysocolla and malachite contain less In this study, two samples are studied for copper extraction than 5% of copper. under various leaching systems consisted of different acids The chemical assay of sample B is shown in Table 4 and oxidants. Sulfuric acid (H2SO4) is a common lixiviant for showing copper grade of 0.601%. Chalcopyrite was the main copper leaching; methanesulfonic acid (CH3SO3H, MSA) is copper-bearing mineral as 1% of chalcopyrite was seen in the widely used for rust and scale removers and electrodeposition XRD analysis result in Table 5. Since the sample was taken [10,11]. Recently, more projects are focused on its from the hypogene zone, it can be deduced that the copper application in the leaching process [12-14]. Hydrogen minerals were mainly copper sulfides. peroxide is adopted as an alternative oxidant to ferric ion. The specific goal of the research is to provide a Table 3. Copper distribution in different minerals of sample A comprehensive study of conichalcite dissolution and compare Copper-bearing mineral Content/% Ratio/% the leaching behavior of two copper minerals. Conichalcite 1.36 70.83 Pyrite 0.4 20.83 2. MATERIALS AND EXPERIMENTAL Chrysocolla 0.07 3.66 METHOD Cu in micas and clays 0.04 2.08 Other Cu 0.03 1.56 Malachite 0.02 1.04 2.1 Materials As-received samples were crushed, ground and dry Table 4. Chemical analysis of sample B. (%) screened to obtain size fraction of 100% passing 2.00 mm Al K Fe S Cu Na Mg and 0.075 mm respectively. Properly sized samples were 5.75 3.79 0.94 0.73 0.601 0.42 0.13 rotary-spilt into 20 g test charges. Chemical analysis of Ba Ti Ca Mo Zn Pb Zr sample A, assayed by ICP-OES following acid digestion, 0.09 0.04 <0.04 0.032 <0.01 0.0007 0.023

Table 5. XRD analysis of sample B. (%) Chalcopyrite Pyrite Quartz K-Feldspar Muscovite Group Kaolinite Plagioclase Biotite Group 1 1 37 35 9 6 11 1 Jiajia Wu, Junmo Ahn, and Jaeheon Lee 3

Fig. 1. Copper recovery of sample A under ferric leaching system with different lixiviants: sulfuric acid; (b) MSA

Fig. 2. Copper recovery of sample A under H2O2 leaching system with different lixiviants: (a) sulfuric acid; (b) MSA

2.2 Experimental method 3. RESULTS AND DISCUSSION Leaching tests were carried out by bottle roll tests. The pulp density of the leach test was 6.25% with 20 g solid and 3.1 Conichalcite leaching test 300 mL solution. The bottle roll test was run for 24 hours at Copper recovery of sample A in sulfuric acid/MSA with ambient temperature and pressure with uncapped bottle. ferric ion is shown in Fig. 1. The copper dissolution Kinetic sample of 5 mL solutions were taken at 1, 6 and 24 kinetics were relatively fast and reached the maximum hours using a syringe-membrane filter (pore size 0.45 µm) and value in five hours. Around 57% and 63% copper were analyzed by AAS (Atomic Absorption Spectrophotometer) for extracted in 0.1 mol/L sulfuric acid and 0.2 mol/L MSA copper assay. Solution lost by sampling was compensated by solution. Copper recovery increased by 7% after adding addition of deionized water. The total leached copper was 0.018 mol/L ferric ion into the sulfuric acid solution and no calculated by the initial solution volume before taking kinetic further increase was observed with 0.054 mol/L ferric ion. samples. In addition, concentration change of lixiviants was However, the copper recovery was not significantly negligible by adding deionized water to compensate the affected by ferric ion when MSA is used as lixiviant. The volume. Sulfuric acid and MSA are used as lixiviants and highest copper extractions about 64% were observed in ferric ion (added as Fe2(SO4)3·5H2O) and hydrogen peroxide both conditions.

(H2O2) are used as oxidants. Dissolution of sample A in H2O2 system is shown in Fig. 4 대한금속 ·재료학회지 제57권 제4호 (2019년 4월)

2. The copper recoveries increased slightly even after 3.0 digestion, and leaching results are shown in Fig. 3. mol/L H2O2 addition, indicating the copper minerals in the The copper grade in the coarse particles (>0.15 mm) was sample A did not show the enhanced leaching behavior by higher than the finer portion, and higher copper recoveries hydrogen peroxide. were obtained. The leaching kinetics of 0.85 mm-2.00 mm Barton et al. [2] reported that the QEMSCAN results particles was slowest because the copper is not fully indicated that conichalcite in the sample A was dissolved liberated, and it took time for the lixiviant to diffuse through after leaching in both conditions. The remaining copper- cracks and fractures of the particle. After leaching tests, the bearing minerals were copper coexisted with pyrite and four residues showed similar copper grade, suggesting that copper minerals under detection limit of QEMSCAN, and the readily dissolved copper were extracted under the they are not oxidized by ferric ion or H2O2 in this test. The leaching condition and the copper sulfide was difficult to be dissolution of conichalcite in acid solution can be expressed dissolved. Further studies about mineral compositions of the as Equation (1). four fractions will be run by QEMSCAN.

+ 2+ 2+ CaCu(AsO4)(OH) + 4H → Ca + Cu + H3AsO4 + H2O 3.2 Chalcopyrite leaching test (1) Unlike sample A, chalcopyrite is reluctant to be dissolved To further study the leaching characteristics of in acidic solution. High temperature and oxidant are required conichalcite, –2.00 mm samples were sieved to 4 different to effectively leach copper from chalcopyrite. size fractions as shown in Table 6. The four samples were Copper extraction with ferric as an oxidant shows lower then leached by 0.1 mol/L sulfuric acid and 0.018 mol/L than 20% as exhibited in Fig. 4. In both leaching systems ferric ion following the same procedure. The Cu contents in (sulfuric acid/MSA with ferric ion), the copper recoveries the heads and residues were analyzed by ICP-OES after acid increased with the presence of 0.018 mol/L ferric ion. However, further increase of copper extraction was not Table 6. Copper assay of sample A before and after leaching observed at higher ferric ion concentration. The highest Size/mm Head/% Residue/% copper recovery can be achieved was 35%. +0.85-2.00 0.46 0.14 According to the mineral analysis from Section 2.2, copper +0.15-0.85 0.54 0.15 existed as chalcopyrite accounts for approximately 50%, and +0.075-0.15 0.33 0.14 the remaining may be copper oxides or sulfides. From Fig. 4, -0.075 0.30 0.16 copper extractions were less than 20% in sulfuric acid and MSA solution without oxidant in 24 hours, indicating the copper oxides, or easily soluble copper minerals, probably account for around 20% of the total copper minerals. The copper recovery increased after ferric ion addition can contribute to the dissolution of some secondary sulfide minerals and chalcopyrite. Theoretically, the reaction between chalcopyrite and ferric ion can be illustrated as Equations (2)-(3) [15].

3+ 2+ 2+ 0 CuFeS2 +4Fe → Cu +5Fe +2S (2)

3+ 2+ 2+ CuFeS2 +4Fe +3O2 +2H2O → Cu +5Fe + 2H2SO4 (3)

Under the conditions used, the reaction (3) is not likely Fig. 3. Copper recovery from different size fractions of sample A. 3+ 0 leaching conditions: 0.01 mol/L H2SO4, 0.018 mol/L Fe happened [16]. The elemental sulfur S will not be oxidized Jiajia Wu, Junmo Ahn, and Jaeheon Lee 5

Fig. 4. Copper recovery of sample B under ferric leaching system with different lixiviants: sulfuric acid; (b) MSA

Fig. 5. Copper recovery of sample B under H2O2 leaching system with different lixiviants: 0.1 mol/L sulfuric acid; (b) 0.3 mol/L MSA

to sulfate and likely forms a passivation layer on chalcopyrite Equation (4). surface, resulting in the low overall copper recovery. H2O2 + H2SO4 → H2SO5 + H2O(4) In leaching systems where H2O2 used as oxidant, as shown in Figure 5, a significant growth in the copper recovery was Therefore, the dissolution kinetics were faster in sulfuric observed with increased H2O2 concentration. When H2O2 acid solution than MSA in the first hour due to the possibly concentration exceeds 3.0 mol/L, over 80% extraction was formed stronger oxidant. achieved. This is due to the strong oxidizing ability of H2O2. The dissolution of copper in the sulfuric acid/MSA and

Further increase H2O2 concentration from 3.0 mol/L to 4.0 H2O2 can be shown as Equations (5) and (6) [19]. mol/L didn’t help a lot in the chalcopyrite dissolution 2CuFeS2 +H2SO4 + 17H2O2 because the strong decomposition of H2O2 at high → 2CuSO4 +Fe2(SO4)3 +18H2O(5) concentration, especially under agitation condition with solids [17]. 2CuFeS2 +10CH3SO3H + 17H2O2 Abou-Yousef [18] reported that a stronger oxidant called → 2Cu(CH3SO3)2 + 2Fe(CH3SO3)3 +4H2SO4 +18H2O(6) “Caro’s acid” (higher oxidizing potential than H2O2) is formed when H2O2 reacts with sulfuric acid, as illustrated in In H2O2 leaching system, chalcopyrite can be effectively 6 대한금속 ·재료학회지 제57권 제4호 (2019년 4월) oxidized and dissolved into the leaching solution. Moreover, (2002). to obtain good leaching results, relatively high H2O2 6. E. M. Cameron, S. M. Hamilton, M. I. Leybourne, G. E. M. concentration should be maintained. Hall, and M. B. Mcclenaghan, Geochemistry: Exploration, Environment, Analysis 4, 7 (2004). 4. CONCLUSION 7. L. Teal and A. Branham, Carlin-Type Gold Deposits Field Conference, p.257, Society of Economic Geologists, Nevada (1997). 1. Approximately 60% copper extraction was achieved in 8. D. F. Briggs, History of the Copper Mountain (Morenci) sulfuric acid/MSA solution from sample A. The main Mining District, Greenlee County, Arizona, p.7, Arizona dissolved minerals are copper oxides, and conichalcite is Geological Survey Contributed Report CR-16-C, Arizona readily dissolved in acid solution. The effect of oxidants is (2016). not significant in the copper extraction. 9. M. S. Enders, Ph. D. Thesis, pp.171-176, The University of 2. Copper recovery of sample B increased with the Arizona, Arizona (2000). presence of oxidants. The majority of chalcopyrite was 10. J.-A. Laffitte and B. Monguillon, US 8574370 B2, p.3, US. oxidized at higher H2O2 concentration, and over 80% copper (2013). extraction was observed with 3.0 mol/L H2O2 and either 11. L. N. Bengoa, P. Pary, M. S. Conconi, and W. A. Egli, lixiviants. Electrochim. Acta 256, 211 (2017). 3. The copper coexisted with pyrite in sample A is almost 12. T. Hidalgo, L. Kuhar, A. Beinlich, and A. Putnis, Miner. 125 insoluble and it was not oxidized by any oxidants in this test. Eng. , 66 (2018). 13. Z. Wu, D. B. Dreisinger, H. Urch, and S. Fassbender, For chalcopyrite in sample B, H2O2 is a better oxidant than Hydrometallurgy 142, 23 (2014). ferric ion. 14. J. Ahn, I. F. Barton, D. Shin, and J. Lee, International REFERENCES Symposium on Materials Processing Fundamentals, 2018 – Phoenix, United States, p.171, Springer, Cham, USA (2018). 1. M. Brininstool and D. M. Flanagan, 2015 Minerals 15. E. M. Córdoba, J. A. Muñozb, M. L. Blázquez, F. González, Yearbook Copper, p.20.8, U.S. Department of the Interior, and A. Ballester, Hydrometallurgy 93, 81 (2008). U.S. Geological Survey, Virginia (2017). 16. C. Klauber, Int. J. Miner. Process. 86, 1 (2008). 2. I. Barton, J. Ahn, and J. Lee, Hydrometallurgy 176, 176 17. E. Y. Yazıcı and H. Deveci, Proceedings of The XIIth (2018). International Mineral Processing Symposium, Cappadocia- 3. H. Zhao, J. Wang, C. Yang, M. Hu, X. Gan, L. Tao, W. Qin, Nevşehir, Turkey, p. 609. Hacettepe University, Turkey and G. Qiu, Hydrometallurgy 151, 141 (2015). (2010). 4. Á. Ruiz-Sánchez and G.T. Lapidus, Hydrometallurgy 169, 18. H. Abou-Yousef, M. El-Sakhawy, and S. Kamel, Industrial 192 (2017). Crops and Products 21, 337 (2005). 5. J. B. Harlan, D. A. Harris, P. M. Mallette, J. W. Norby, J. C. 19. M. M. Antonijevic, Z. D. Jankovic, and M. D. Dimitrijevic, Rota, and J. J. Sagar, Geology and mineralization of the Hydrometallurgy 71, 329 (2004). Maggie Creek district, p. 115, NBMG Bulletin, Nevada